On L∞L^\infty estimates for Monge-Amp\`ere and Hessian equations on nef classes

The PDE approach developed earlier by the first three authors for $L^\infty$ estimates for fully non-linear equations on K\"ahler manifolds is shown to apply as well to Monge-Amp\`ere and Hessian equations on nef classes. In particular, one obtains a new proof of the estimates of Boucksom-Eyssidieux-Guedj-Zeriahi and Fu-Guo-Song for the Monge-Amp\`ere equation, together with their generalization to Hessian equations

Research on surface roughness of circular arc cut by ASJ

Izrađen je potpuni faktorijalni plan eksperimenata za istraživanje učinaka tlaka mlaza, reznog posmaka i polumjera kružnog luka na površinsku hrapavost kružnog luka rezanog mlazom abrazivne otopine - abrasive suspension jet (ASJ). Ortogonalnim planom eksperimenata analizirala se veličina djelovanja parametara na hrapavost rezne površine na različitim dubinama. Smanjivanje brzine prijelaza je najučinkovitija metoda za smanjenje površinske hrapavosti. Uz to, usporedbom topografije rezne površine s onom pomoću AWJ, ustanovilo se da je površina sastavljena od četiri zone: inicijalna zona, glatka zona, prijelazna zona i gruba zona. Konačno, primijenjena je metoda multipne linearne regresije za postavljanje modela hrapavosti površine na različitim dubinama, što se eksperimentima potvrdilo kao pouzdano. Zaključci mogu poslužiti kao teorijski vodič za poboljšanje učinkovitosti rezanja pomoću ASJ.Full factorial design of experiments was developed in order to investigate the effects of jet pressure, cutting feed, and circular arc radius upon the one response variable surface roughness of circular arc cut by abrasive suspension jet (ASJ). And orthogonal design of experiments was used for analysing the magnitude of effects of parameters on roughness of the cutting surface at different depths. Slowing down the traverse speed is the most effective method to reduce the surface roughness. In addition, comparing the topography of the cutting surface with that by AWJ, it is found that the surface also consists of four zones: initial zone, smooth zone, transition zone and rough zone. Finally, the multiple linear regression was employed to establish the model of cutting surface roughness at different depths, which was proved to be reliable by experiments. The conclusions can provide theoretical guidance for improving the cutting efficiency of ASJ

Effects of Velocity Profiles on Measuring Accuracy of Transit-Time Ultrasonic Flowmeter

Ultrasonic wave carries the information for flowing velocity when it is propagating in flowing fluids. Flowrate can be obtained by measuring the propagation time of ultrasonic wave. The principle of transit-time ultrasonic flowmeters used today was based on that the velocity is uniform along the propagation path of the ultrasonic wave. However, it is well known that the velocity profiles in a pipe are not uniform both in laminar flow and turbulent flow. Emphasis on the effects of velocity profiles across the pipe on the propagation time of ultrasonic wave, theoretical flowrate correction factors considering the real velocity profile were proposed for laminar and turbulent flow to obtain higher accuracy. Experiment data of ultrasonic flowmeter and weighting method are compared to verify the proposed theoretical correction factors. The average relative error of proposed correction factor is determined to be 0.976% for laminar flow and 0.25% for turbulent flow

Study on Dynamic Strain Distribution in Rock Broken by Abrasive Slurry Jet

To reveal the stress and strain field in rock under abrasive slurry jet (ASJ) impacting, this paper carried out experiments to measure the dynamic rock strain using a novel strain measurement approach, which is the non-contact strain measurement system. Moreover, it was compared with the theoretical analysis of stress propagation in rock. The results showed that dynamic strain will propagate within rock in the form of spherical waves, whose maximum value is proportional to the jet pressure and inversely proportional to the square of the propagation distance. In the process of ASJ impacting rock, strain will increase from zero to a maximum value in milliseconds. Dynamic strain in rock is fluctuates due to the release of internal stress caused by the rock crushing, which can reflect that rock will be broken by ASJ in the form of stepped-failure. The paper reveals the dynamic strain distribution in rock broken by ASJ and provides a new idea and method for studying the rock failure mechanism under ASJ impacting

Rheological behaviors of coal slime produced by filter-pressing

It is an effective way to use coal slime as fuel for circulating fluidized bed boilers, which will not only solve its pollution to the environment, but also turn waste to treasure. In order to provide basic technical information for transportation of coal slime from the coal preparation plant to the boiler, this paper experimentally studied the rheological behaviors of coal slime produced by filter-pressing. By using a rotational viscometer, the influences of water content, temperature, and shear time on the rheological behaviors of coal slime were investigated. Experimental results show that the coal slime will behave like Bingham plastics with low water content and like Bingham pseudo-plastics with 37.5% water content, while like pseudo-plastics with 40% water content. This indicates that the water content of coal slime must be controlled in consideration of both transportation resistance and combustion efficiency. Study results also show that, the apparent viscosity of coal slime at 5 °C is about 1.5–1.7 times of that at 40 °C for water contents 32%–37.5%, while the influence of temperature can be neglected when the water content is 40%. With increasing of water content, the influences of shear time on the apparent viscosity of coal slime becomes less. When the water content is more than 30%, the effect of shear time is negligible. It indicates that water content has the most important influence on the rheological behaviors of coal slime. There must be an optimal water content in considering conveying resistance and combustion efficiency. The environmental temperature must also be considered in coal slime transportation. Keywords: Coal slime, Rheological behavior, Non-Newtonian fluid, Apparent viscosit

A Study on Processing Defects and Parameter Optimization in Abrasive Suspension Jet Cutting of Carbon-Fiber-Reinforced Plastics

Abrasive suspension jet (ASJ), an accurate cold-cutting technology, can address traditional processing issues relating to carbon-fiber-reinforced plastics (CFRPs) like tool wear, interlayer delamination, large heat-affected zone, and low surface roughness. This study employed the use of an ASJ to cut CFRPs and an ultra-depth optical microscope to scan the cut surface to analyze interlayer delamination, surface roughness, kerf taper, and shoulder damage. Regression analysis was conducted to establish a prediction model for cutting quality based on surface roughness, kerf taper, and shoulder damage. Various types of CFRP cutting quality were analyzed using jet parameters. It was found that the use of ASJ to process CFRP results in the following defects: The range of surface roughness variation is from 0.112 μm to 0.144 μm. Surface roughness is most influenced by stand-off distance, followed by traverse speed and jet pressure. The range of kerf taper variation is from 4.737° to 10.1°. Kerf taper is most influenced by stand-off distance, followed by jet pressure and traverse speed. The range of shoulder damage variation is from 3.384 μm2 to 10 μm2. Shoulder damage is most influenced by jet pressure, followed by traverse speed and stand-off distance. A prediction model for cutting quality was developed based on surface roughness, kerf taper, and shoulder damage, providing data support for ASJ cutting of CFRPs. The optimal parameter combination is a stand-off distance of 1 mm, a jet pressure of 30 MPa, and a traverse speed of 30 mm/min

Study on ASJ Cutting of TC18, Based upon Multivariate Nonlinear Regression and SA-BP-AGA

TC18 titanium alloy has been widely applied, but is considered as a difficult machining material. Taking the kerf angle as the quality criterion, this paper studied the cutting performance of TC18 by the use of an abrasive slurry jet (ASJ), based upon multivariate nonlinear regression and SA-BP-AGA. Cutting experiments were carried out according to the Taguchi orthogonal method. The experimental factors included traverse speed, standoff distance, pressure and slurry concentration, with five levels set, respectively. Meanwhile, a characterization method of the major influencing factors was proposed. A multiple nonlinear regression model and a back propagation artificial neural network (BP) prediction model, based on adaptive genetic algorithm (AGA), were established. The reliability was verified by statistics equations for the 22 groups of the fitting or training model and the three groups of experimental results. The BP-AGA and Simulated annealing algorithm (SA) were used to form a set of prediction optimization systems, called integrated SA-BP-AGA. Finally, the results showed that the main factor influencing the kerf angle is the slurry concentration. BP-AGA is easier to model, offers better robustness and is more accurate than a multivariate nonlinear regression model. The best kerf angle can be predicted by the integration system. The study results can improve the performance for the machining of TC18 by ASJ

The Development of an Optimized Evaluation System for Improving Coal Dust Suppression Efficiency using Aqueous Solution Sprays

Coal dust has been a serious hazard for the global coal mining industry, and water spray has been commonly used for coal dust suppression. To effectively optimize the dust control efficiency of the aqueous solution, an evaluation system of the solution wettability was investigated and constructed. Different static wetting features (surface tension, contact angle, spreading work, sink time, capillary rise weight and drop penetration time) and dust control efficiency of the solution were studied under different surfactant concentrations. The relationship between static wetting features and an evaluation system was analyzed by the analytic hierarchy process. Additionally, the correlations between static wetting parameters and dust suppression efficiency were investigated. The results indicated that the surfactant concentrations causing the optimal values of different static wetting parameters were inconsistent, and it is not suitable for optimizing the solution wettability based on a single wetting parameter. The weight coefficients of surface tension (0.3265) and sink time (0.2383) on the evaluation system were better than that of other parameters. Additionally, three wetting parameters (surface tension, sink time and spreading work) that have the best correlations with dust control efficiency were used as simple and efficient evaluation indexes to construct the evaluation system. Based on the developed evaluation system, the optimal surfactant concentration was determined